An apparatus and a method for regenerating a particulate filter of an exhaust system of an internal combustion engine is known, for example, from US 2003/0200742.
Particulate materials (PM) within exhaust gas of a vehicle are mainly exhausted from diesel engines that generally control power output by a mixing ratio of air and fuel. Diesel engines increase fuel supply with respect to a quantity of air and burn the fuel when instantaneous high power is needed. When this occurs, a large amount of vehicle exhaust pollutants may be generated by incomplete combustion of the fuel due to a shortage of air. Further, during combustion in a diesel engine, a locally dense amount of PM may appear since the time of spraying fuel into a combustion chamber is extremely quick compared to a resultant increase in intake air quantity, and thus a large amount of vehicle exhaust pollutants may be generated. Generally, PM has a minute diameter and includes a large amount of soluble organic materials in addition to carbon particles. Research into human body hazards is currently proceeding based upon recent reports of this being a factor of lung cancer.
DPF traps use a technology of collecting and burning PM that is exhausted from diesel engines, and can reduce PM by more than 80%. However, the technology has drawbacks of high cost and uncertainty of durability. Technology of DPF traps is mainly classified as collecting PM, and regenerating and controlling technology.
DPF trap methods are classified as active regeneration methods and passive regeneration methods according to the method of burning PM during a regeneration process. The active regeneration method actively applies heat for regeneration using an electric heater, a burner, or a throttle, and the passive regeneration method regenerates a filter with additives or oxidation catalysts using the heat of the exhaust gas. Since a vehicle that is primarily city driven emits exhaust gas of a low temperature, and thus cannot obtain desired performance with only a passive regeneration method, a combination method using both active regeneration and passive regeneration is currently generally adopted.
The DPF technology of the passive regeneration method lowers the passive regeneration temperature of PM from 650° C. to 300° C. using catalysts or additives. However, the passive regeneration method is difficult to apply directly to city buses since city buses run at a low speed and stop often, and thus the temperature of the exhaust gas is low or usually below 250° C. The method is also difficult to apply to mid-size or small diesel vehicles of which the temperature of the exhaust gas is low in the range of from 150° C. to 200° C.
When the active regeneration method is applied using an electric heater, the cost of required electric power becomes excessively high. When the active regeneration method is applied using a burner that has a simple structure, it is difficult to control the operation according to the condition of oxygen within the exhaust gas, which varies depending on operating conditions since the burner uses oxygen within the exhaust gas. The method of throttling or injecting fuel additives lowers the oxidation temperature of PM at the catalyst, but the method needs a device for throttling on the intake/exhaust pipe and has a possibility of secondary contamination by the additives.